In today's semiconductor integrated circuits, the diameter of the via plug formed with copper (Cu) inside of an insulating film between layers is reduced from 65 nm to 45 nm along with the miniaturization. It is expected that the diameter of the via plug will be further reduced to 32 nm or 22 nm in recent future.
As the semiconductor integrated circuits are miniaturized, it is difficult to form a bather metal film or a Cu seed layer by the conventional PVD method in a miniaturized via hole or a wiring groove in view of the step coverage. Accordingly, a film forming technology by the MOCVD method or the ALD method is studied in which an improved step coverage can be realized at a low temperature that does not damage the insulating film between layers formed with a low dielectric material (low-K material).
However, the MOCVD method and the ALD method generally use an organic metal as a base material where metal atoms are combined with an organic group. As a result, impurities tend to reside in the formed film, and thus, the quality of the film is not stable even if the step coverage looks satisfactory. For example, when a Cu seed layer is formed on a metal film of Ta bather by the MOCVD method, the formed Cu seed layer tends to generate a condensation thereby making it difficult to form a Cu seed layer that stably covers the Ta barrier film with a uniform film thickness. When an electrolysis plating is performed using the seed layer that generated the condensation as an electrode, potential defects may be included in the Cu layer charged at the wiring groove or the via hole. As a result, problem occurs such as the increase of the electric resistance as well as the electro-migration tolerance or a deterioration of the stress-migration tolerance.
Thus, a method has been recently suggested where a barrier metal film or a Cu seed layer is formed directly on the insulating film between layers by the MOCVD technology of a metal film using a metal carbonyl base material. Metal carbonyl base material is readily dissociated at a relatively low temperature to form a metal layer, and the CO, which is the ligand of metal carbonyl base material, does not reside in the formed film and immediately discharged to outside of the film forming reaction system. As a result, the barrier metal film or the Cu seed layer can be formed with a good quality having extremely low impurities. Using this method, a W film can be formed using, for example, W(C)6, as a barrier metal layer, or a ruthenium (Ru) film can be formed using, for example, Ru3(CO)12, as the Cu seed layer.